LIDAR 3D design using a polygon mirror

ABSTRACT

In one embodiment, a LIDAR device of an autonomous driving vehicle (ADV) includes an array of light emitters to emit a number of light beams to sense a physical range associated with a target. The LIDAR device further includes a prism-shaped mirror assembly having a plurality of joining faces acting as reflective surfaces and a bottom base face. The rotatable platform is configured to rotate with respect to a vertical axis perpendicular to the bottom base face. The light emitters are configured to project the light beams onto the reflective surfaces of the mirror assembly, which are deflected towards the target. The mirror assembly rotates along with the rotatable platform while the array of light emitters remains steady. The LIDAR device further includes one or more light detectors to receive at least a portion of the light beams reflected from the target.

TECHNICAL FIELD

Embodiments of the present disclosure relate generally to operating autonomous driving vehicles. More particularly, embodiments of the disclosure relate to a LIDAR device utilized in autonomous driving vehicles.

BACKGROUND

Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.

LIDAR techniques have been widely utilized in military, geography, oceanography, and in the latest decade, autonomous driving vehicles. Apart from others, LIDAR's applications in autonomous driving vehicles have been hindered by the high cost. A LIDAR device can estimate a distance to an object while scanning through a scene to assemble a point cloud representing a reflective surface of the object. Individual points in the point cloud can be determined by transmitting a laser pulse and detecting a returning pulse, if any, reflected from the object, and determining the distance to the object according to the time delay between the transmitted pulse and the reception of the reflected pulse. A laser or lasers can be rapidly and repeatedly scanned across a scene to provide continuous real-time information on distances to reflective objects in the scene.

A traditional LIDAR device typically utilizes a mirror that spins or rotates in two directions in order to cover the entire 360 degree environment. In addition, a traditional LIDAR device requires a light emitter and light detector to rotate along with the mirror, which consumes more power to drive the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.

FIG. 1 is a block diagram illustrating a networked system according to one embodiment.

FIG. 2 is a block diagram illustrating an example of an autonomous vehicle according to one embodiment.

FIG. 3 is a block diagram illustrating an example of a perception and planning system used with an autonomous vehicle according to one embodiment.

FIG. 4 shows a typical LIDAR mounting configuration.

FIG. 5 is a diagram illustrating an example LIDAR subassembly according to one embodiment.

FIG. 6 is a diagram illustrating an expanded scanning angle range according to one embodiment.

FIGS. 7A and 7B are diagrams illustrating example LIDAR implementations according to embodiments.

FIG. 8 is a flow diagram illustrating a process of operating a LIDAR device according to one embodiment.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosures will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosures.

Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment.

Accordingly, an approximately prism-shaped mirror assembly (hereafter referred to simply as a “prism-shaped mirror assembly”) comprising a plurality of reflective surfaces is utilized in a LIDAR device, where the mirror assembly spins in a single orientation to cover both the horizontal and vertical scanning, while the light emitters and the light detectors remain steady. The LIDAR structure is simpler and more effective, and consumes less power since the light emitters and light detectors remain steady.

In one embodiment, the prism-shaped mirror assembly may be approximately a triangular prism in shape with the bottom base face adjoined to a rotatable platform and the three joining faces acting as reflective surfaces. The reflective surfaces may be coated with reflective material according to any conventional technique, so that they may properly reflect incoming light. The angle between any two reflective surfaces may be approximately 60 degrees. The three reflective surfaces may not all form right angles with the bottom base face, and may be angled slightly differently with respect to the bottom base face. For example, the angles between the three reflective surfaces and the bottom base face may be 89 degrees, 90 degrees, and 91 degrees, respectively. The exact angles do not limit the disclosure. For example, in one embodiment, a first reflective surface may form an angle in the range of 80 degrees to 90 degrees (exclusive) with the bottom base face; a second reflective surface may form a right angle (90 degrees) with the bottom base face; and a third reflective surface may form an angle in the range of 90 degrees to 100 degrees (exclusive) with the bottom base face.

According to one aspect, there is an array of light transmitters (TX) (e.g., 4 or more light transmitters, such as 16 light transmitters) configured to emit a plurality of light beams. Given the orientation of the reflective surfaces of the rotating mirror assembly, the light beams can be scattered across a large scanning angular range. As a result, the overall scanning area in all time will be significantly increased.

According to one embodiment, a LIDAR device of an autonomous driving vehicle (ADV) includes an array of light emitters to emit a number of light beams to sense a physical range associated with a target. The LIDAR device further includes a prism-shaped mirror assembly supported by a rotatable platform, the joining faces of the mirror assembly forming different angles with respect to a bottom base face and acting as reflective surfaces. The rotatable platform is configured to rotate with respect to a vertical axis perpendicular to the bottom base face of the mirror assembly. The light emitters are configured to project the light beams onto the reflective surfaces of the mirror assembly, which are deflected towards the target. The mirror assembly rotates along with the rotatable platform while the array of light emitters remains steady. The LIDAR device further includes one or more light detectors to receive at least a portion of the light beams reflected from the target.

In one embodiment, the bottom base face of the prism-shaped mirror assembly is positioned in parallel with a ground floor on which the ADV is driving and the reflective surfaces of the mirror assembly is tilted upwardly from the bottom base face according to predetermined different angles. The light beams are projected onto the reflective surfaces of the mirror assembly and substantially perpendicular to the bottom base face. In one embodiment, the array of light emitters includes a relative large number of light emitters (e.g., 4 or more light emitters, such as 16 light emitters).

According to a further aspect of the invention, an ADV includes a LIDAR device as described above and a perception and planning system. The perception and planning system is configured to perceive a driving environment surrounding the ADV based on LIDAR sensor data provided by the LIDAR device and to control the ADV to navigate through the driving environment.

In one embodiment, the light beams emitted by the light emitters are deflected by a mirror before reaching the mirror assembly.

In one embodiment, the light beams emitted by the light emitters pass through an aperture in a mirror before reaching the mirror assembly, and the light beams reflected by the target are deflected by the mirror before reaching the light detectors. In one embodiment, the light beams emitted by the light emitters pass through a collimating lens before reaching the aperture.

FIG. 1 is a block diagram illustrating an autonomous vehicle network configuration according to one embodiment of the disclosure. Referring to FIG. 1, network configuration 100 includes autonomous vehicle 101 that may be communicatively coupled to one or more servers 103-104 over a network 102. Although there is one autonomous vehicle shown, multiple autonomous vehicles can be coupled to each other and/or coupled to servers 103-104 over network 102. Network 102 may be any type of networks such as a local area network (LAN), a wide area network (WAN) such as the Internet, a cellular network, a satellite network, or a combination thereof, wired or wireless. Server(s) 103-104 may be any kind of servers or a cluster of servers, such as Web or cloud servers, application servers, backend servers, or a combination thereof. Servers 103-104 may be data analytics servers, content servers, traffic information servers, map and point of interest (MPOI) servers, or location servers, etc.

An autonomous vehicle refers to a vehicle that can be configured to in an autonomous mode in which the vehicle navigates through an environment with little or no input from a driver. Such an autonomous vehicle can include a sensor system having one or more sensors that are configured to detect information about the environment in which the vehicle operates. The vehicle and its associated controller(s) use the detected information to navigate through the environment. Autonomous vehicle 101 can operate in a manual mode, a full autonomous mode, or a partial autonomous mode.

In one embodiment, autonomous vehicle 101 includes, but is not limited to, perception and planning system 110, vehicle control system 111, wireless communication system 112, user interface system 113, infotainment system 114, and sensor system 115. Autonomous vehicle 101 may further include certain common components included in ordinary vehicles, such as, an engine, wheels, steering wheel, transmission, etc., which may be controlled by vehicle control system 111 and/or perception and planning system 110 using a variety of communication signals and/or commands, such as, for example, acceleration signals or commands, deceleration signals or commands, steering signals or commands, braking signals or commands, etc.

Components 110-115 may be communicatively coupled to each other via an interconnect, a bus, a network, or a combination thereof. For example, components 110-115 may be communicatively coupled to each other via a controller area network (CAN) bus. A CAN bus is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts.

Referring now to FIG. 2, in one embodiment, sensor system 115 includes, but it is not limited to, one or more cameras 211, global positioning system (GPS) unit 212, inertial measurement unit (IMU) 213, radar unit 214, and a light detection and range (LIDAR) unit 215. GPS system 212 may include a transceiver operable to provide information regarding the position of the autonomous vehicle. IMU unit 213 may sense position and orientation changes of the autonomous vehicle based on inertial acceleration. Radar unit 214 may represent a system that utilizes radio signals to sense objects within the local environment of the autonomous vehicle. In some embodiments, in addition to sensing objects, radar unit 214 may additionally sense the speed and/or heading of the objects. LIDAR unit 215 may sense objects in the environment in which the autonomous vehicle is located using lasers. LIDAR unit 215 could include one or more laser sources, a laser scanner, and one or more detectors, among other system components. Cameras 211 may include one or more devices to capture images of the environment surrounding the autonomous vehicle. Cameras 211 may be still cameras and/or video cameras. A camera may be mechanically movable, for example, by mounting the camera on a rotating and/or tilting a platform.

Sensor system 115 may further include other sensors, such as, a sonar sensor, an infrared sensor, a steering sensor, a throttle sensor, a braking sensor, and an audio sensor (e.g., microphone). An audio sensor may be configured to capture sound from the environment surrounding the autonomous vehicle. A steering sensor may be configured to sense the steering angle of a steering wheel, wheels of the vehicle, or a combination thereof. A throttle sensor and a braking sensor sense the throttle position and braking position of the vehicle, respectively. In some situations, a throttle sensor and a braking sensor may be integrated as an integrated throttle/braking sensor.

In one embodiment, vehicle control system 111 includes, but is not limited to, steering unit 201, throttle unit 202 (also referred to as an acceleration unit), and braking unit 203. Steering unit 201 is to adjust the direction or heading of the vehicle. Throttle unit 202 is to control the speed of the motor or engine that in turn control the speed and acceleration of the vehicle. Braking unit 203 is to decelerate the vehicle by providing friction to slow the wheels or tires of the vehicle. Note that the components as shown in FIG. 2 may be implemented in hardware, software, or a combination thereof.

Referring back to FIG. 1, wireless communication system 112 is to allow communication between autonomous vehicle 101 and external systems, such as devices, sensors, other vehicles, etc. For example, wireless communication system 112 can wirelessly communicate with one or more devices directly or via a communication network, such as servers 103-104 over network 102. Wireless communication system 112 can use any cellular communication network or a wireless local area network (WLAN), e.g., using WiFi to communicate with another component or system. Wireless communication system 112 could communicate directly with a device (e.g., a mobile device of a passenger, a display device, a speaker within vehicle 101), for example, using an infrared link, Bluetooth, etc. User interface system 113 may be part of peripheral devices implemented within vehicle 101 including, for example, a keyboard, a touch screen display device, a microphone, and a speaker, etc.

Some or all of the functions of autonomous vehicle 101 may be controlled or managed by perception and planning system 110, especially when operating in an autonomous driving mode. Perception and planning system 110 includes the necessary hardware (e.g., processor(s), memory, storage) and software (e.g., operating system, planning and routing programs) to receive information from sensor system 115, control system 111, wireless communication system 112, and/or user interface system 113, process the received information, plan a route or path from a starting point to a destination point, and then drive vehicle 101 based on the planning and control information. Alternatively, perception and planning system 110 may be integrated with vehicle control system 111.

For example, a user as a passenger may specify a starting location and a destination of a trip, for example, via a user interface. Perception and planning system 110 obtains the trip related data. For example, perception and planning system 110 may obtain location and route information from an MPOI server, which may be a part of servers 103-104. The location server provides location services and the MPOI server provides map services and the POIs of certain locations. Alternatively, such location and MPOI information may be cached locally in a persistent storage device of perception and planning system 110.

While autonomous vehicle 101 is moving along the route, perception and planning system 110 may also obtain real-time traffic information from a traffic information system or server (TIS). Note that servers 103-104 may be operated by a third party entity. Alternatively, the functionalities of servers 103-104 may be integrated with perception and planning system 110. Based on the real-time traffic information, MPOI information, and location information, as well as real-time local environment data detected or sensed by sensor system 115 (e.g., obstacles, objects, nearby vehicles), perception and planning system 110 can plan an optimal route and drive vehicle 101, for example, via control system 111, according to the planned route to reach the specified destination safely and efficiently.

Server 103 may be a data analytics system to perform data analytics services for a variety of clients. In one embodiment, data analytics system 103 includes data collector 121 and machine learning engine 122. Data collector 121 collects driving statistics 123 from a variety of vehicles, either autonomous vehicles or regular vehicles driven by human drivers. Driving statistics 123 include information indicating the driving commands (e.g., throttle, brake, steering commands) issued and responses of the vehicles (e.g., speeds, accelerations, decelerations, directions) captured by sensors of the vehicles at different points in time. Driving statistics 123 may further include information describing the driving environments at different points in time, such as, for example, routes (including starting and destination locations), MPOIs, road conditions, weather conditions, etc.

Based on driving statistics 123, machine learning engine 122 generates or trains a set of rules, algorithms, and/or predictive models 124 for a variety of purposes. In one embodiment, algorithms 124 may include an algorithm to process LIDAR sensor data for perception using a LIDAR device described throughout this application. Algorithms 124 can then be uploaded on ADVs to be utilized during autonomous driving in real-time.

FIG. 3 is a block diagram illustrating an example of a perception and planning system used with an autonomous vehicle according to one embodiment. System 300 may be implemented as a part of autonomous vehicle 101 of FIG. 1 including, but is not limited to, perception and planning system 110, control system 111, and sensor system 115. Referring to FIG. 3, perception and planning system 110 includes, but is not limited to, localization module 301, perception module 302, prediction module 303, decision module 304, planning module 305, control module 306, and routing module 307.

Some or all of modules 301-307 may be implemented in software, hardware, or a combination thereof. For example, these modules may be installed in persistent storage device 352, loaded into memory 351, and executed by one or more processors (not shown). Note that some or all of these modules may be communicatively coupled to or integrated with some or all modules of vehicle control system 111 of FIG. 2. Some of modules 301-307 may be integrated together as an integrated module.

Localization module 301 determines a current location of autonomous vehicle 300 (e.g., leveraging GPS unit 212) and manages any data related to a trip or route of a user. Localization module 301 (also referred to as a map and route module) manages any data related to a trip or route of a user. A user may log in and specify a starting location and a destination of a trip, for example, via a user interface. Localization module 301 communicates with other components of autonomous vehicle 300, such as map and route information 311, to obtain the trip related data. For example, localization module 301 may obtain location and route information from a location server and a map and POI (MPOI) server. A location server provides location services and an MPOI server provides map services and the POIs of certain locations, which may be cached as part of map and route information 311. While autonomous vehicle 300 is moving along the route, localization module 301 may also obtain real-time traffic information from a traffic information system or server.

Based on the sensor data provided by sensor system 115 and localization information obtained by localization module 301, a perception of the surrounding environment is determined by perception module 302. The perception information may represent what an ordinary driver would perceive surrounding a vehicle in which the driver is driving. The perception can include the lane configuration, traffic light signals, a relative position of another vehicle, a pedestrian, a building, crosswalk, or other traffic related signs (e.g., stop signs, yield signs), etc., for example, in a form of an object. The lane configuration includes information describing a lane or lanes, such as, for example, a shape of the lane (e.g., straight or curvature), a width of the lane, how many lanes in a road, one-way or two-way lane, merging or splitting lanes, exiting lane, etc.

Perception module 302 may include a computer vision system or functionalities of a computer vision system to process and analyze images captured by one or more cameras in order to identify objects and/or features in the environment of autonomous vehicle. The objects can include traffic signals, road way boundaries, other vehicles, pedestrians, and/or obstacles, etc. The computer vision system may use an object recognition algorithm, video tracking, and other computer vision techniques. In some embodiments, the computer vision system can map an environment, track objects, and estimate the speed of objects, etc. Perception module 302 can also detect objects based on other sensors data provided by other sensors such as a radar and/or LIDAR.

For each of the objects, prediction module 303 predicts what the object will behave under the circumstances. The prediction is performed based on the perception data perceiving the driving environment at the point in time in view of a set of map/rout information 311 and traffic rules 312. For example, if the object is a vehicle at an opposing direction and the current driving environment includes an intersection, prediction module 303 will predict whether the vehicle will likely move straight forward or make a turn. If the perception data indicates that the intersection has no traffic light, prediction module 303 may predict that the vehicle may have to fully stop prior to enter the intersection. If the perception data indicates that the vehicle is currently at a left-turn only lane or a right-turn only lane, prediction module 303 may predict that the vehicle will more likely make a left turn or right turn respectively.

For each of the objects, decision module 304 makes a decision regarding how to handle the object. For example, for a particular object (e.g., another vehicle in a crossing route) as well as its metadata describing the object (e.g., a speed, direction, turning angle), decision module 304 decides how to encounter the object (e.g., overtake, yield, stop, pass). Decision module 304 may make such decisions according to a set of rules such as traffic rules or driving rules 312, which may be stored in persistent storage device 352.

Routing module 307 is configured to provide one or more routes or paths from a starting point to a destination point. For a given trip from a start location to a destination location, for example, received from a user, routing module 307 obtains route and map information 311 and determines all possible routes or paths from the starting location to reach the destination location. Routing module 307 may generate a reference line in a form of a topographic map for each of the routes it determines from the starting location to reach the destination location. A reference line refers to an ideal route or path without any interference from others such as other vehicles, obstacles, or traffic condition. That is, if there is no other vehicle, pedestrians, or obstacles on the road, an ADV should exactly or closely follows the reference line. The topographic maps are then provided to decision module 304 and/or planning module 305. Decision module 304 and/or planning module 305 examine all of the possible routes to select and modify one of the most optimal routes in view of other data provided by other modules such as traffic conditions from localization module 301, driving environment perceived by perception module 302, and traffic condition predicted by prediction module 303. The actual path or route for controlling the ADV may be close to or different from the reference line provided by routing module 307 dependent upon the specific driving environment at the point in time.

Based on a decision for each of the objects perceived, planning module 305 plans a path or route for the autonomous vehicle, as well as driving parameters (e.g., distance, speed, and/or turning angle), using a reference line provided by routing module 307 as a basis. That is, for a given object, decision module 304 decides what to do with the object, while planning module 305 determines how to do it. For example, for a given object, decision module 304 may decide to pass the object, while planning module 305 may determine whether to pass on the left side or right side of the object. Planning and control data is generated by planning module 305 including information describing how vehicle 300 would move in a next moving cycle (e.g., next route/path segment). For example, the planning and control data may instruct vehicle 300 to move 10 meters at a speed of 30 mile per hour (mph), then change to a right lane at the speed of 25 mph.

Based on the planning and control data, control module 306 controls and drives the autonomous vehicle, by sending proper commands or signals to vehicle control system 111, according to a route or path defined by the planning and control data. The planning and control data include sufficient information to drive the vehicle from a first point to a second point of a route or path using appropriate vehicle settings or driving parameters (e.g., throttle, braking, steering commands) at different points in time along the path or route.

In one embodiment, the planning phase is performed in a number of planning cycles, also referred to as driving cycles, such as, for example, in every time interval of 100 milliseconds (ms). For each of the planning cycles or driving cycles, one or more control commands will be issued based on the planning and control data. That is, for every 100 ms, planning module 305 plans a next route segment or path segment, for example, including a target position and the time required for the ADV to reach the target position. Alternatively, planning module 305 may further specify the specific speed, direction, and/or steering angle, etc. In one embodiment, planning module 305 plans a route segment or path segment for the next predetermined period of time such as 5 seconds. For each planning cycle, planning module 305 plans a target position for the current cycle (e.g., next 5 seconds) based on a target position planned in a previous cycle. Control module 306 then generates one or more control commands (e.g., throttle, brake, steering control commands) based on the planning and control data of the current cycle.

Note that decision module 304 and planning module 305 may be integrated as an integrated module. Decision module 304/planning module 305 may include a navigation system or functionalities of a navigation system to determine a driving path for the autonomous vehicle. For example, the navigation system may determine a series of speeds and directional headings to affect movement of the autonomous vehicle along a path that substantially avoids perceived obstacles while generally advancing the autonomous vehicle along a roadway-based path leading to an ultimate destination. The destination may be set according to user inputs via user interface system 113. The navigation system may update the driving path dynamically while the autonomous vehicle is in operation. The navigation system can incorporate data from a GPS system and one or more maps so as to determine the driving path for the autonomous vehicle.

FIG. 4 shows a typical LIDAR configuration with respect to an autonomous driving vehicle. As shown in FIG. 4, LIDAR device 215 is typically mounted on the top of ADV 300. The LIDAR device is configured to spin, for example, according to spinning direction 401, such that LIDAR device 215 can scan the entire 360 degree environment. LIDAR device 215 includes at least one light emitter therein (not shown) to emit a light beam towards target 402. LIDAR device 215 further includes at least one light detector or light sensor (not shown) to receive and detect the light beam reflected from target 402.

Referring to FIG. 5, a diagram illustrating an example LIDAR subassembly 500 according to one embodiment is shown. A triangular prism-shaped mirror assembly 501 is provided, comprising a bottom base face (not shown) adjoined to a rotatable platform 503 and three joining faces acting as reflective surfaces 502. The reflective surfaces 502 tilt from the bottom base face at different angles. In the example shown, the angles formed between the reflective surfaces 502 and the bottom base face are 89 degrees, 90 degrees, and 91 degrees, respectively. It should be appreciated that the exact angles do not limit the disclosure. For example, in one embodiment, a first reflective surface 502 may form an angle in the range of 80 degrees to 90 degrees (exclusive) with the bottom base face; a second reflective surface may form a right angle (90 degrees) with the bottom base face; and a third reflective surface may form an angle in the range of 90 degrees to 100 degrees (exclusive) with the bottom base face. The rotatable platform 503 is configured to rotate with respect to a vertical axis 504 perpendicular to the bottom base face of the mirror assembly. Thus, during normal operations, the mirror assembly rotates with the rotatable platform 503 with respect to a vertical axis 504.

Referring to FIG. 6, a diagram 600 illustrating an expanded scanning angle range according to one embodiment is shown. Because the reflective surfaces 502 tilt upwardly from the bottom base face of the mirror assembly at different angles (e.g., 89 degrees, 90 degrees, and 91 degrees, respectively), the scanning angle range is expanded, especially when an array of light transmitters comprising a relative large number of transmitter (e.g., 16 transmitters) is utilized together with the prism-shaped mirror assembly.

Referring to FIG. 7A, a diagram illustrating an example LIDAR implementation 700A according to one embodiment is shown. Light beams transmitted by the light transmitters 710 pass through a converging lens 732, and are then deflected by a small mirror 730 toward the rotating mirror assembly 501. Next, the mirror assembly 501 deflects the light beams toward the target 402. Light reflected from the target 402 travels toward the mirror assembly 501, and is then deflected by the mirror assembly 501 toward the light detectors 720. Before the reflected light reaches the light detectors 720, it passes through a converging lens 736. It should be appreciated that although the mirror 730 is in the path of the reflected light, it causes negligible interference with the reflected light due to its small size. Signals generated by the light detectors 720 as a result of the reflected light can thereafter be processed using conventional LIDAR techniques.

Referring to FIG. 7B, a diagram illustrating another example LIDAR implementation 700B according to one embodiment is shown. Light beams transmitted by the light transmitters 710 pass through an aperture or cutout portion 746 of a mirror 740, and reach the rotating mirror assembly 501 directly. In one embodiment, light beams transmitted by the light transmitters 710 pass through a collimating lens 742 before reaching the aperture or cutout portion 746, where the collimating lens 742 make the light beams parallel. Next, the mirror assembly 501 deflects the light beams toward the target 402. Light reflected from the target 402 travels toward the mirror assembly 501, and is then deflected by the mirror assembly 501 toward the mirror 740. The mirror 740 deflects the reflected light toward the light detector 720. Before the reflected light reaches the light detectors 720, it passes through a converging lens 744. Signals generated by the light detectors 720 as a result of the reflected light can thereafter be processed using conventional LIDAR techniques.

It should be appreciated that the LIDAR implementations illustrated in FIGS. 7A and 7B effect a reduction in the interference between light beams generated by the light transmitters and the light reflected by the target. Accordingly, performance of the LIDAR is improved.

FIG. 8 is a flow diagram illustrating a process of operating a LIDAR device according to one embodiment. Process 800 may be performed by processing logic which may include software, hardware, or a combination thereof. Referring to FIG. 8, in operation 810, processing logic emits, using an array of a plurality of light emitters, a plurality of light beams to sense a physical range of a target. In operation 820, a prism-shaped mirror assembly is provided, where the prism-shaped mirror assembly includes a plurality of joining faces acting as reflective surfaces and a bottom base face supported by a rotatable platform. In operation 830, the rotatable platform is rotated together with the prism-shaped mirror assembly with respect to a vertical axis perpendicular to the bottom base face, while the light emitters remain steady. In operation 840, the light beams are projected onto the reflective surfaces of the prism-shaped mirror assembly, which are deflected by the reflective surfaces towards the target. In operation 850, at least a portion of the light beams is received reflected from the target by one or more light detectors.

Note that some or all of the components as shown and described above may be implemented in software, hardware, or a combination thereof. For example, such components can be implemented as software installed and stored in a persistent storage device, which can be loaded and executed in a memory by a processor (not shown) to carry out the processes or operations described throughout this application. Alternatively, such components can be implemented as executable code programmed or embedded into dedicated hardware such as an integrated circuit (e.g., an application specific IC or ASIC), a digital signal processor (DSP), or a field programmable gate array (FPGA), which can be accessed via a corresponding driver and/or operating system from an application. Furthermore, such components can be implemented as specific hardware logic in a processor or processor core as part of an instruction set accessible by a software component via one or more specific instructions.

Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as those set forth in the claims below, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

Embodiments of the disclosure also relate to an apparatus for performing the operations herein. Such a computer program is stored in a non-transitory computer readable medium. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices).

The processes or methods depicted in the preceding figures may be performed by processing logic that comprises hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination of both. Although the processes or methods are described above in terms of some sequential operations, it should be appreciated that some of the operations described may be performed in a different order. Moreover, some operations may be performed in parallel rather than sequentially.

Embodiments of the present disclosure are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the disclosure as described herein.

In the foregoing specification, embodiments of the disclosure have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. 

What is claimed is:
 1. A light detection and range (LIDAR) device utilized in an autonomous driving vehicle (ADV), the LIDAR device comprising: an array of light emitters to emit a plurality of light beams to sense a physical range associated with a target; a prism-shaped mirror assembly having a plurality of joining faces acting as reflective surfaces and a bottom base face; a rotatable platform supporting the bottom base face of the prism-shaped mirror assembly, the rotatable platform capable of rotating with respect to a vertical axis perpendicular to the bottom base face, wherein the light emitters project the light beams onto the reflective surfaces, which are deflected towards the target, and wherein the prism-shaped mirror assembly rotates along with the rotatable platform while the array of light emitters remain steady; and one or more light detectors to receive at least a portion of the light beams reflected from the target, wherein the prism-shaped mirror assembly is approximately a triangular prism in shape, wherein the bottom base face of the prism-shaped mirror assembly is positioned in parallel with a ground floor on which the ADV is driving, wherein the reflective surfaces are tilted upwardly from the bottom base face according to predetermined angles that are different from each other, and wherein one of the reflective surfaces forms an angle of 90 degrees with the bottom base face.
 2. The LIDAR device of claim 1, wherein a first reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 80 degrees to 90 degrees, exclusive, wherein a second reflective surface of the reflective surfaces forms an angle of 90 degrees with the bottom base face, and wherein a third reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 90 degrees to 100 degrees, exclusive.
 3. The LIDAR device of claim 1, wherein the array of light emitters comprise 4 or more light emitters.
 4. The LIDAR device of claim 1, wherein the light beams emitted by the light emitters are deflected by a mirror before reaching the mirror assembly.
 5. The LIDAR device of claim 1, wherein the light beams emitted by the light emitters pass through an aperture in a mirror before reaching the mirror assembly, and the light beams reflected by the target are deflected by the mirror before reaching the light detectors.
 6. The LIDAR device of claim 5, wherein the light beams emitted by the light emitters pass through a collimating lens before reaching the aperture.
 7. An autonomous driving vehicle (ADV), comprising: a light detection and range (LIDAR) device, where in the LIDAR device comprises an array of light emitters to emit a plurality of light beams to sense a physical range associated with a target, a prism-shaped mirror assembly having a plurality of joining faces acting as reflective surfaces and a bottom base face, a rotatable platform supporting the bottom base face of the prism-shaped mirror assembly, the rotatable platform capable of rotating with respect to a vertical axis perpendicular to the bottom base face, wherein the light emitters project the light beams onto the reflective surfaces, which are deflected towards the target, and wherein the prism-shaped mirror assembly rotates along with the rotatable platform while the array of light emitters remain steady, and one or more light detectors to receive at least a portion of the light beams reflected from the target; and a perception and planning system coupled to the LIDAR device to perceive a driving environment surrounding the autonomous driving vehicle based on LIDAR sensor data provided by the LIDAR device and to control the autonomous driving vehicle to navigate the driving environment, wherein the prism-shaped mirror assembly is approximately a triangular prism in shape, wherein the bottom base face of the prism-shaped mirror assembly is positioned in parallel with a ground floor on which the ADV is driving, wherein the reflective surfaces are tilted upwardly from the bottom base face according to predetermined angles that are different from each other, and wherein one of the reflective surfaces forms an angle of 90 degrees with the bottom base face.
 8. The autonomous driving vehicle of claim 7, wherein a first reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 80 degrees to 90 degrees, exclusive, wherein a second reflective surface of the reflective surfaces forms an angle of 90 degrees with the bottom base face, and wherein a third reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 90 degrees to 100 degrees, exclusive.
 9. The autonomous driving vehicle of claim 7, wherein the array of light emitters comprise 4 or more light emitters.
 10. The autonomous driving vehicle of claim 7, wherein the light beams emitted by the light emitters are deflected by a mirror before reaching the mirror assembly.
 11. The autonomous driving vehicle of claim 7, wherein the light beams emitted by the light emitters pass through an aperture in a mirror before reaching the mirror assembly, and the light beams reflected by the target are deflected by the mirror before reaching the light detectors.
 12. The autonomous driving vehicle of claim 11, wherein the light beams emitted by the light emitters pass through a collimating lens before reaching the aperture.
 13. A machine-implemented method for operating a LIDAR device of an autonomous driving vehicle (ADV), the method comprising: emitting using an array of light emitters a plurality of light beams to sense a physical range associated with a target; providing a prism-shaped mirror assembly having a plurality of joining faces acting as reflective surfaces and a bottom base face; rotating a rotatable platform supporting the bottom base face of the mirror assembly, the rotatable platform capable of rotating with respect to a vertical axis perpendicular to the bottom base face, wherein the mirror assembly rotates along with the rotatable platform while the array of light emitters remain steady; projecting the light beams onto the reflective surfaces of the mirror assembly, wherein the light beams are deflected by the reflective surfaces towards the target; and receiving using one or more light detectors at least a portion of the light beams reflected from the target, wherein the prism-shaped mirror assembly is approximately a triangular prism in shape, wherein the bottom base face of the prism-shaped mirror assembly is positioned in parallel with a ground floor on which the ADV is driving, wherein the reflective surfaces are tilted upwardly from the bottom base face according to predetermined angles that are different from each other, and wherein one of the reflective surfaces forms an angle of 90 degrees with the bottom base face.
 14. The machine-implemented method of claim 13, wherein a first reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 80 degrees to 90 degrees, exclusive, wherein a second reflective surface of the reflective surfaces forms an angle of 90 degrees with the bottom base face, and wherein a third reflective surface of the reflective surfaces forms an angle with the bottom base face in a range of 90 degrees to 100 degrees, exclusive.
 15. The machine-implemented method of claim 13, wherein the array of light emitters comprise 4 or more light emitters.
 16. The machine-implemented method of claim 13, wherein the light beams emitted by the light emitters are deflected by a mirror before reaching the mirror assembly.
 17. The machine-implemented method of claim 13, wherein the light beams emitted by the light emitters pass through an aperture in a mirror before reaching the mirror assembly, and the light beams reflected by the target are deflected by the mirror before reaching the light detectors.
 18. The machine-implemented method of claim 17, wherein the light beams emitted by the light emitters pass through a collimating lens before reaching the aperture. 